Production of a variety of sizes of the panels are usually existed in a panel plant. In order to maintain the quality of mass-produced products, a light-on test on the different sizes of products need to be performed before being sold to exclude defective products. A panel light-on apparatus is necessary while performing analysis on the defective products. The panel light-on apparatus used nowadays is shown in FIG. 1. A workbench 10′ is disposed on a supporting member 1′ to hold and secure a tested panel 13′, and a backlight unit 11′ is disposed at bottom of the workbench 10′ to provide backlight to the tested panel 13′. The tested panel 13′ is controlled by a test signal to display white image, red image, green image, blue image, black image, grayscale image, etc. on the entire display area respectively for observing by the inspectors. Therefore, the light-on testing procedure is only for confirming the adverse phenomena.